U.S. Pat. Nos. 4,395,865 and 4,429,515, both to Davis, Jr., disclose a riding mower chassis for a front mounted mower, which chassis has laterally spaced front traction wheels and a castering dual rear wheel that swivels about a vertical axis intersecting the longitudinal centerline of the chassis. Each of the front traction wheels is driven by its own hydraulic motor, and these motors are independently controllable from a pair of levers accessible to the operator. The disclosed arrangement provides the machine with a so-called zero turning radius whereby the front mounted mower can be moved virtually sideward. The attainment of such extreme maneuverability is expensive because of the need for a hydraulic system that must include a fluid pump, the two hydraulic motors, and control valves for the motors. For many users, therefore, the cost of this machine is not justified by its maneuverability advantages, which are needed only in special situations. Furthermore, the machine may have a tendency to tip over on relatively steep slopes, owing to its tricycle wheel arrangement. It is probable, too, that most users of a riding mower would prefer to steer it with the familiar steering wheel, which can be manipulated with one hand, rather than with a pair of steering levers which present an unfamiliar arrangement that they must learn to operate.
U.S. Pat. No. 4,384,443 discloses a riding mower chassis for a group of reel mowers, having laterally spaced front traction wheels and laterally spaced steerable rear wheels, the steering of which is controlled from a steering wheel at the front of the chassis. The mowers are hydraulically driven, and the hydraulic system provides for driving the front wheels and also for transmitting steering inputs from the steering wheel to the rear wheels. Since the hydraulic system was needed in this machine for other purposes, it was available to solve the problem of transmitting steering inputs along substantially the whole length of the chassis, but in a machine wherein the traction wheels and mower can be driven through inexpensive mechanical transmissions, it would obviously be impractical to provide a hydraulic system merely for steering control.
On a mower-carrying chassis having laterally spaced steerable wheels as well as laterally spaced traction wheels, the steerable wheels are preferably arranged for limited up and down movement relative to the chassis, so that all four wheels will remain engaged with the ground on irregular terrain, to ensure good driving and steering traction. For such up and down displacement the steerable wheels are connected with the chassis frame by means of parallelogram linkages, as disclosed in U.S. Pat. No. 4,416,109, or--as is more usual--are mounted on opposite ends of an axle that is pivoted to the chassis at its midpoint to swing about a central fore-and-aft extending axis. Pivoted axle arrangements are disclosed, for example, in U.S. Pat. Nos. 2,924,928, 3,250,064 and--in a somewhat unusual arrangement--in U.S. Pat. No. 3,440,740. In all of these cases the steerable wheels that had such so-called floating mountings were at the front of the chassis, and since the steering wheel or the like was directly over those wheels, or nearly so, it was possible to provide sturdy, simple and compact means for transmitting steering inputs to those wheels from the manually actuated steering controller.
With a front mounted mower, the arrangement comprising front traction wheels and rear steerable wheels provides for a significantly shorter turning radius than the more conventional rear wheel drive, even though it does not afford the zero-radius turning capability of machines having a castered rear wheel.
One might assume that there would be no great problem in providing a mechanical connection between steerable rear wheels and a steering controller at the front of the chassis. Indeed, U.S. Pat. No. 4,325,211, which contains a rather sketchy disclosure of a front drive-rear steered mower-carrying unit says: "Steering wheel 18 is coupled to rear wheels 14 through any standard linkage." But there is no indication that the steerable rear wheels of this unit were floatingly mounted, and it will be apparent that floating mounting of the steerable rear wheels complicates the problem of adapting a "standard linkage" for steering control of such wheels.
If a steering linkage comprises a rigid rod-like member that extends lengthwise between the steering controller and the floatingly mounted rear wheels, that member must either be connected to the steering linkage on a vertical plane containing the rear axle pivot axis or must be jointed to accommodate up and down tilting of the rear wheel assembly. If the connection is made at the pivot axis, then the steering linkage must include means for accomplishing a rather awkward translation of fore-and-aft lengthwise movements of the rod-like member into swiveling of the rear wheels about their steering knuckles.
In every case a satisfactory mechanical connection between a steering controller at the front of the chassis and steerable rear wheels must meet other requirements. It should be located along parts of the chassis where it will not be in the way of a person using the machine or working around it and will not be disturbed by shrubbery or the like brushing against the machine during mowing. Thus, it should preferably be located wholly at the underside of the chassis, but at a level high enough to avoid entanglement with tall grass, weeds and the like. However, this desirable location is one that is already occupied to a substantial extent by transmission means for connecting the engine with the traction wheels and with the mower, and by other parts of the machine. The steering linkage or connection obviously should not interfere with these other parts of the machine. Needless to say, it should be simple, sturdy and reliable as well as inexpensive.
Apparently it has not been obvious to those skilled in the art how to meet all of these requirements, since the applicant knows of no disclosure of a front wheel drive mower chassis having floatingly mounted steerable rear wheels wherein steering of the rear wheels was controlled other than hydraulically. The absence of such a machine is not due to lack of incentive for providing it. The maneuverability of a front drive-rear steered machine is well known, the importance of floatingly mounting the steerable wheels is also well known, and the cost advantages of a simple mechanical connection over a hydraulic system are obvious.